The adult rat (Rattus norvegicus) has a prominent 24-hr variation in body temperative (Tb). Althrough subject to external influences, the circadinan temperature rhythm is endogenously generated and persists when environmental cues are held constant. The hypothalamus appears to be critically involved in the CTR system, but the underlying neural circuitry remains to be worked out. Very little is known regarding developmental influences on the emergence and expression of the CTR in rats. I am proposing a program of research to examine maternal, environmental, and neural contributions to the development of the CTR in rats. Continuous 10-min-interval measurements of telemetered Tb from 8 or 10 Days of age to adulthood will be used to determine period, phase, and amplitude changes in the CTR over this time period. The combupterized data collection system is currently in operation in our lab. I plan experiments which will help answer such questions as: 1) Does the dam impose a CTR on her pups that is reflected in the development of their CTR? 2) how does the CTR develop from Day 1 in pups deprived of maternal influences? 3) Do light, temperature, and feeding cycles affect CTR emergence? 4) what role do various hypothalamic areas play in CTR ontogeny? 5) Are there circadian variations in temperature regulation during development? Information regarding these issues and others is presently unavailable. It is known, however, that loss of temporal organization among biological systems characterizes the aging process in humans and animals. It has also been suggested that a serious thermoregulatory deficit observed in elderly persons, accidental hypothermia, may be a result of circadian desynchronization of thermoregulatory mechanisms in the face of thermal challenge. Our knowledge of rhythm dissociations and aging will be enhanced by a clearer understanding of the ontogenetical processes that contribute to temporal organization in developing organisms. The CTR is intimately linked with rhythmical patterns observed in other physiological systems. Light shed on CTR development will reflect on rhythm emergence in rodents in general and may illuminate maturetional processes and environmental influences critical to normal functioning.